Previously, methods and apparatus have been developed for harvesting ice from column type evaporators in which a gas such as Freon is utilized as a refrigerant. The gas, after passing through a heat exchanger and compressor, enters a chamber formed between two concentric tubular members. This chamber is sealed at both ends, thus forcing the refrigerant gas to enter or exit the chamber only at two designated locations. Simultaneously as the gas is discharged into the chamber and while expanding therein, water is introduced to flow along the outer exposed surfaces of the concentric tubular members and transformed into ice due to the heat absorption from the concentric tubular members occasioned by the expansion of the refrigerant gas. After the water is transformed into ice, the gas that has become a non-refrigerant through heat absorption is recirculated between the tubular members. This warms the surfaces of the tubular members and eventually enables the ice to be removed. In previously known evaporators of the vertical column type, the tubular members tend to cool excessively at the regions nearest the discharge of the refrigerant from the cold gas or refrigerant inlet. A relatively large temperature differential may occur on the surfaces of the tubular members, causing the formation of uneven ice thicknesses during the freezing cycle. Consequently, the ice becomes difficult to remove from the evaporator.
To avoid this problem, an improved column type evaporator, disclosed in U.S. Re. Pat. No. 26,693 to Paul D. Campbell, reissued Oct. 14, 1969, utilizes separate refrigerant and hot gas lines, extending through the evaporator chamber and terminating adjacent each other at a lower region of the chamber. A gas deflection element connected to the hot gas line is in the form of an annular ring disposed to cause hot gas to flow toward the discharge end of the refrigerant line. The hot gas thus preheats the discharge end of the refrigerant line. During the freezing cycle, rapid expansion of the refrigerant as it leaves the discharge end of the refrigerant line is moderated to obtain more uniform ice thickness throughout the length of the evaporator.
While the aforesaid evaporator is generally more efficient than other evaporators of which I am aware, ice formed at the upper part of the evaporator chamber requires a substantial period of time to release from and slide off the outer and inner tubular members since the hot gas entering the chamber from the bottom has given up most of its latent heat prior to reaching the upper part of the chamber. Thus, a relatively long ice harvest cycle is required, and the power requirements of the evaporator is also relatively high.
During the freezing cycle, another disadvantage associated with the above evaporator is that of ice bridging to a top plate connecting upper ends of the inner and outer tubular members together. This ice bridging problem also occurs along the upper walls of the tubular members where water is initially sprayed, resulting in a formation of ice having an uneven thickness within the upper region of the evaporator.
It is accordingly an object of the present invention to provide an improved column type evaporator for ice manufacturing machines.
Another object of the present invention is to improve the ice harvest cycle in a column type evaporator by preheating upper parts of the inner and outer tubular members so that ice releases from and slides off the members relatively quickly during the harvest cycle.
Still another object is to provide an improved column type evaporator wherein ice bridging to the top plate in connecting the tubular members as well as ice bridging along the upper surfaces of the tubular members is prevented to encourage formation of an ice layer of a uniform thickness.
Yet a further object of the invention is to increase ice production by reducing both freezing and ice harvesting cycle times, thereby conserving power.
Still another object of the invention is to achieve the foregoing objects without requiring additional parts or equipment.